When contact lenses and intraocular lenses, insertion instruments for intraocular lenses, endoscopes, catheters, tubes, and various similar classes of medical instruments are used, the surface of the medical instrument frequently comes into direct contact with biological tissue, with the two sliding against one another. However, because most medical instruments are made of materials such as metal or resin, during contact with biological tissue, lubricity is low and hydrophilicity is lacking, thereby posing a risk of problems such as friction-induced deterioration of the medical instrument, or inflammation.
For this reason, techniques have been contemplated in the past to improve lubricity and hydrophilicity of medical instrument surfaces by subjecting the surface of a medical instrument such as a catheter or intraocular lens insertion instrument to a coating process with any of various classes of hydrophilic polymers, as disclosed in Patent Documents 1 to 4.
However, it is not an easy matter to form a stable coating of a hydrophilic polymer on the surface of a hydrophobic base material such as metal or polypropylene, and inability to achieve satisfactory coating strength, endurance, or lubricity was a recurring problem.
Specifically, according to the coating technique disclosed in Patent Document 1 and Patent Document 2, the coating layer formed on the medical instrument surface is produced from a hydrophilic polymer, and a resultant problem is that if the coating comes into contact with water, the polymer elutes into solution so that the coating effect is lost. Other problems include poor cohesion between the coating layer and the coated surface resulting in inability to produce a uniform coating layer, as well as premature peeling of the coating layer as a whole.
The technique disclosed in Patent Document 3 attempts to improve coating durability by forming a primary layer of a polymer such as polyurethane on the surface of the medical instrument, in this case a stent; and then producing a secondary layer of a polymer with a heparin molecule bonded thereto. However, because the process requires forming two coating layers, a resultant problem was increased labor and cost associated with the coating process.
Meanwhile, an intraocular lens insertion instrument, which is another type of medical instrument, is designed to plunge a compactly folded intraocular lens into the eye through an insertion tube of fine tube shape in order to insert the intraocular lens into the eye through a tiny incision made in ocular tissue such as the cornea. However, even if an ophthalmic viscoelastic material is used as a lubricant, a problem encountered during the plunging operation was that, as a result of improper levels or lack of lubricity between the intraocular lens and the inner surface of the insertion tube made of hydrophobic material, the intraocular lens does not plunge in smoothly.
For this reason it was contemplated to improve lubricity with the intraocular lens by producing a coating layer inside the intraocular lens insertion instrument as disclosed in Patent Document 4. However, because a hydrophilic polymer such as water-soluble cellulose is employed as a component of the coating layer, the problems encountered were like those in the techniques disclosed in Patent Documents 1 and 2, namely, weak bonding and cohesion between the coating layer and the hydrophobic surface of the insertion instrument, resulting in a tendency of the coating layer to delaminate. An additional problem was that when the coating layer comes into contact with water during use, water-soluble coating components rapidly elute into solution so that surface lubricity is not sustained. Also, because the coating liquid is a water-based solution, it tends to clump due to high surface energy, making it difficult to form a uniform thin coating layer. For this reason, the intraocular lens insertion instrument was not provided with sufficient lubricity or hydrophilicity needed for pushing out the lens.
Patent Document 1: JP-T 2006-510756
Patent Document 2: JP-T 2005-537097
Patent Document 3: JP-T 2006-500987
Patent Document 4: JP-T 10-512172